Wireless digital networks, such as networks operating under the current Electrical and Electronics Engineers (IEEE) 802.11 standards, are spreading in their popularity and availability. In a typical WLAN environment, a client device will select one of the access points (APs) in the WLAN to associate with. Generally, the client device will select the AP from which the client device receives a signal with strongest signal strength compared with signals received from other APs in the WLAN.
Such selection usually works well for the first time when the client device joins the WLAN. However, as time progresses, some events may lead to this initial selection of AP by the client device no longer being an optimal selection. For example, the client device may roam to a new location that is far away from the AP. As another example, the AP may have been overloaded with too many other client devices. As yet another example, the wireless channel on which the client device communicates with the AP may be experiencing significant interference or noises. Usually when such events happen, the client device would start to experience poor network connectivity. However, the client device may be unwilling or unable to disassociate with the initial AP and associate with a new AP in the WLAN responsive to such events. Note that, when a client device selects a sub-optimal AP, the poor selection not only affects the client device's own network connectivity, but also affect the AP's performance and other client the network connectivity of other client devices in the WLAN.
In a centralized system, a central network controller device could help the client device select an optimal AP and instruct to the APs to facilitate the client device to be connected with the selected AP. However, in a distributed system where there is no centralized network control device, there are at least two problems that prevent an AP from helping the client device to select an optimal AP in the WLAN. First, a “thin” AP has limited computational resource, and mainly forwards packets between wireless and wired networks. Thus, a “thin” AP is unable to help the client to select an optimal AP.
Second, a “fat” AP, on the other hand, can provide much broad functionality. One of multiple “fat” APs from an AP cluster may be self-elected as a master AP to provide network management of other APs (hereinafter referred to as “slave APs”) in the same cluster of APs. Nevertheless, a slave AP often does not communicate with a master AP before a client device completes the association phrase. Thus, the slave AP may only communicate with the master AP after the client device is already connected with the WLAN. Therefore, the master AP has limited ability to influence the slave AP on the optimal AP selection for the client device due to this lack of communication during client device association and authentication process. Hence, it is desirable to have a lightweight solution that allows an AP to help the client select an optimal AP to connect in a distributed WLAN system.